Re: NEC-LIST: cross field antennas

Grant,

        I was going to attach a photo of the antenna but when I
dragged out the camera an expensive smell came out of it when I
connected it to the PC ... oh well. I am attaching instead a diagram
of one version of the antenna I have here. It is in jpeg format ... I
use this one at 28 Mhz. Please note the following ....

It is my belief that only the two central plates in the CFA ( H plates
) contribute to any radiation characteristics.( my phasing network
fell off the E plates under load and the remote FSM increased ! )
Hence the simpler design of my version .. the hidden element I was
alluding to was removal not addition.

The plates are constructed from 1 mm aluminium.

The central wire is fixed to the centre of the top plate and passes
through a 5 cm hole in the lower plate.

The variable cap is set to 220 pF for operation at 26 to 30 Mhz.

All connections in 1.5 mm wire and as short as possible ( found that
even 1 cm of extra wire on transformer connection causes marked change
in performance.)

The coax feed must be looped through a suitable ferrite 4 to 6 times
to prevent feedline radiation. The position of this choke on the
feedline will change the tuning characteristic of the antenna.

The coax feed must leave the antenna along a perpendicular axis to the
lower plate surface or RF coupling will result.

No metallic structures within close proximity of plates ( especially
top plate )

I am interested in the feedpoint impedance between the lower plate and
the wire at the point it passes through the lower plate. Are you also
able to plot the phase of the E field between the plates versus the
magnitude and phase of the current on the wire over the test frequency
range ... 26 - 30 Mhz?

Regards.

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From: Grant Bingeman <DrBingo_at_compuserve.com>
To: paul moody <paulmoody_at_onaustralia.com.au>
Subject: Re: NEC-LIST: cross field antennas
Date: Saturday, February 13, 1999 4:31 AM

Paul, I'd be happy to model it using the latest NEC4.1, if you wish.
But you will have to send me exact dimensions.

Also, the latest Egypt CFA has what they call a conical extension.
I'll bet they would be very interested in your "prior art." That is,
who invented it, you or them? I hope you kept good notes, dated and
witnessed by others. Of course, their extension may not be your
matcher.

Grant Bingeman
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[I've removed the diagram of the CFA in jpg format from the e-mail
because it's not really suitable for distribution through the mailing
list. Anyone who would like a copy should ask Paul Moody to send them
a copy. - DGM]
Received on Thu Feb 18 1999 - 05:08:10 EST